Epothilone A (R═H) and Epothilone B (R═CH3) are produced by Sorangium cellulosum strain So ce 90, the structures of which are shown below, and were the first of several epothilones to be isolated and characterized. Höfle et al., 1996, Angew. Chem. Int. Ed. Engl. 35(13/14): 1567–1569.

Epothilone A and epothilone B possess many of the advantageous properties of taxol. As a result, there is significant interest in these and structurally related compounds as potential chemotherapeutic agents. The desoxy counterparts of epothilones A and B are known as epothilone C (R═H) and epothilone D (R═CH3), and also exhibit similar anti-tumor activity but with less cytotoxicity. The structures of epothilones C and D are shown below.

Other epothilone compounds have since been described. These include other naturally occurring epothilones such as the 39 compounds isolated from Sorangium cellulosum So ce 90 of which epothilones A, B, C, and D together account for approximately 98.9% of the total epothilones produced (WO 99/65913) and epothilone analogs derived from de novo chemical synthesis (see e.g., WO 98/25929; WO 99/01124; WO 99/02514; WO 99/07692; WO 99/43653;WO 99/54319; WO 99/67253; WO 00/37473; WO 00/50423; and WO 00/66589). Epothilone compounds derived from bioconversion also have been disclosed. For example, PCT publication WO 00/39276 describes the use of Amycolata autotrophica ATCC 35203 to convert epothilone B to epothilone F (which differs from epothilone B by the addition of a hydroxyl at C-21).
Due to the increasing interest in epothilones as anti-cancer agents, novel derivatives of these compounds are needed and desired to more fully develop their therapeutic potential.